The present invention relates to a positioning stage having a vibration suppressor, which is used in an apparatus for manufacturing semiconductor products, an inspection apparatus for semiconductors, and various precise measuring apparatus.
In recent years, a positioning stage having a high precision (for instance, a positioning precision of 0.1 microns or less) has been employed in various manufacturing apparatus and inspection apparatuses of semiconductor products. A positioning stage of such type which has been heretofore used, is generally constructed, for instance, as illustrated in FIGS. 1 to 3.
In these figures, reference character a designates a foundation, a machine base c is provided above this foundation a by the intermediary of resilient means b, and further, on this machine base c a first stage d is provided so as to be movable in predetermined directions (the directions indicated by arrows Ad). Reference character e designates a first driving device for moving the first stage d, and in general, a servomotor is used therefor. In addition, reference character f designates a screw shaft which engages the first stage d to move the same. The shaft rotated by the servomotor e and is constrained so as to be not movable in the axial direction but to be allowed only to rotate. Reference character g designates rails along which the first stage d can slidably move. Furthermore, reference character h designates a second stage provided on the first stage d so as to be movable along rails k in the directions at right angles to the directions of movement of the first stage d. Reference character i designates a second driving device provided on the first stage for moving the second stage h, which is similar to the first driving device e provided on the machine base c, and reference character j designates a screw shaft formed in the same manner as the screw shaft f. The above-mentioned resilient means b is, for example, an air spring, and the purpose of providing such resilient member b is to prevent vibration from being transmitted from the ground surface l to the respective stages d and h.
In order to move the first stage d on the machine base c, a force is applied to the first stage d by means of the first driving device e to accelerate the first stage d, or in order to stop the first stage d, a force directed in the opposite direction is applied to the first stage d by means of the first driving device e to decelerate the first stage d. In this case, a reaction force for the force exerted upon the first stage for acceleration or deceleration, is exerted upon the machine base c. Since the machine base c is supported by the intermediary of the resilient means b, when it is applied with the reaction force of acceleration or deceleration, it moves in the opposite direction to or in the same direction as the direction of movement of the first stage d. In this way, during the period when the first stage is being accelerated or decelerated, the machine base c is displaced to a position that is different from its original position, although the displacement is very small. When this acceleration or deceleration has been terminated, the reaction force exerted upon the machine base c would disappear, and therefore, the resilient means b tends to restore from its resiliently deformed state towards its original unstrained state. Hence, as will be obvious from the theory of mechanical vibration, vibration having a vibration characteristic determined by the mass of the machine base c and the mechanical structure mounted thereon and the elastic constant of the resilient means b, would be excited. In this way, after the first stage d has been moved (that is, acceleration and deceleration has been finished), vibration is excited in the machine base c, and since this vibration sustains even after stoppage of the first stage d, this phenomenon would be harmful for the apparatus provided with the positioning stages.
The above-mentioned vibration-exciting phenomenon occurs similarly with respect to the second stage h also, that is, as a result of movement of the second stage h, vibration is excited in the machine base c via the first stage d, the direction of vibration being at right angles to the direction of the vibration excited by the movement of the first atage d, and this phenomenon would be also harmful for the apparatus provided with the positioning stage.
It is to be noted, depending upon the type of apparatus embodying the present invention, it is necessitated to move a specimen only in a one-dimensional manner, and in this basic case, the above-mentioned second stage and second driving device therefore are not provided but only the first stage and the associated driving device therefor are employed. It will be self-evident that such a basic apparatus also has the same disadvantage with respect to the direction of movement of the single stage.
Heretofore, various countermeasures have been undertaken for preventing or suppressing the vibration excited by a reaction force of the force generated to move a positioning stage.
These countermeasures are enumerated as follows:
(A) The mass of the machine base c is selected to be quite large compared to the masses of the respective stages d and h. PA1 (B) The moving speeds of the respective stages are slowed down to reduce the acceleration and deceleration. PA1 (C) The resilient means b is additionally associated with a damer such as an oil damper to quickly damp the excited vibration.
However, every one of these countermeasures involves shortcomings and various problems would arise in practice even if any one of the countermeasures is practiced. For instance, according to the countermeasure (A) above, the weight of the machine base c must be made very heavy, and so, a problem would remain with respect to handling and manufacturing cost of the subject apparatus. According to the countermeasure (B) above, since the operation speed is reduced, the efficiency of the work for production or inspection is lowered, and so, this is basically unfavorable for practical use. According to the countermeasure (C), since the vibration is made to disappear after it has been generated, a considerable time is required before vibration is completely stopped. Moreover, due to the existence of the oil damper, there is a fear that during a normal operation of the apparatus, vibration may be transmitted to the positioning stage externally through the oil damper.
It is therefore one object of the present invention to provide a positioning stage which is free from the disadvantages or problems in the prior art as described above.
A more specific object of the present invention is to provide a positioning stage having a vibration suppressor which prevents or almost suppresses the above-mentioned vibration from occurring in a machine base.
Another object of the present invention is to provide a positioning stage having a vibration suppressor in which an oil damper is not used, the moving speed of the stages is not slowed down and the mass of the machine base is not enlarged.
Still another object of the present invention is to provide a positioning stage having a vibration suppressor, in which a plurality of stages adapted to be moved in different directions are provided and the vibration suppressor effectively suppresses the aforementioned vibration from occurring in the machine base upon any movement of the stages.